Neutrino mass hierarchy and three-flavor spectral splits of supernova neutrinos

TL;DR

This paper investigates how three-flavor neutrino effects influence spectral splits in supernova neutrinos, revealing hierarchy-dependent modifications and the conditions under which these effects alter the flavor evolution during supernova cooling.

Contribution

It systematically analyzes the impact of three-flavor effects on spectral splits, highlighting hierarchy-dependent differences and the conditions affecting flavor stability.

Findings

In inverted hierarchy, high-energy spectral splits are suppressed and transferred to other flavors.

In normal hierarchy, three-flavor effects cause minor deviations from two-flavor predictions.

Imperfect adiabaticity leads to smearing of spectral swap features.

Abstract

It was recently realized that three-flavor effects could peculiarly modify the development of spectral splits induced by collective oscillations, for supernova neutrinos emitted during the cooling phase of a protoneutron star. We systematically explore this case, explaining how the impact of these three-flavor effects depends on the ordering of the neutrino masses. In inverted mass hierarchy, the solar mass splitting gives rise to instabilities in regions of the (anti)neutrino energy spectra that were otherwise stable under the leading two-flavor evolution governed by the atmospheric mass splitting and by the 1-3 mixing angle. As a consequence, the high-energy spectral splits found in the electron (anti)neutrino spectra disappear, and are transferred to other flavors. Imperfect adiabaticity leads to smearing of spectral swap features. In normal mass hierarchy, the three-flavor and the two-flavor instabilities act in the same region of the neutrino energy spectrum, leading to only minor departures from the two-flavor treatment.